Dangerous and Venomous Aquarium Fish

Supplement to the July 2008 AFI article Living Dangerously.

How Many Are There?
Until recently, scientists estimated that only approximately 200 or so species of venomous fish existed. Medical records documenting incidents formed the basis for this conclusion (Handwerk, 2005). Recent studies have demonstrated that this estimate was significantly low; the revised number exceeds 1,200 species.

This new number comes from studying the phylogeny of spiny-rayed fish, which allows researchers to predict the distribution of specific characteristics among clades of animals. A survey of 233 fish species was used to create a new phylogenetic tree for spiny-rayed fish, and 102 specimens were dissected to test the accuracy of these predictions. More than 60 proved venomous, confirming the new predictions (Smith and Wheeler, 2006).

The possibility of new pharmacological agents motivated most studies of venomous fish; but the proteins are difficult to work with, indicating uncertain prospects for fish venom in medicine. Further complicating matters, fish venom varies widely in composition, making basic knowledge about one type of venom different than others (Smith, personal communication). Another factor confusing the issue relates to the age of the animals, with some being venomous as juveniles but not as adults. There are exceptions, such as the blue tang (Paracanthurus hepatus), which keeps its envenomating ability throughout its life (Smith, personal communication).

Envenomating Saltwater Vertebrates*

Stingrays (Order Dasyatidae)
• Description of Danger: Stinger is a razor-sharp, barbed or serrated cartilaginous spine which grows from the ray's whiplike tail (like a fingernail) and can grow as long as 14.5 inches. On the underside of the spine are two grooves containing venom-secreting glandular tissue. The entire spine is covered with a thin layer of skin called the integumentary sheath, in which venom is concentrated.
• Effects: The stinger often breaks off in the wound, which is not fatal to the stingray, and it will be regrown. Contact with the stinger causes local trauma (from the cut itself), pain and swelling from the venom, and possible later infection from bacteria on parts of the stinger left in the wound. Immediate injuries to humans include but are not limited to: poisoning, punctures, severed arteries and possibly death. Fatal stings, such as that which killed Australian naturalist and television personality Steve Irwin in September 2006, are extremely rare.
• Treatment: Apply near-scalding water to ease pain (possibly by denaturing the complex venom protein, possibly by easing vasoconstriction). Pain normally lasts up to 48 hours, but is most severe in the first 30 to 60 minutes and may be accompanied by nausea, fatigue, headaches, fever and chills. All stingray injuries should be medically assessed; the wound needs to be thoroughly cleaned, and surgical exploration is often required to remove any barb fragments remaining in the wound.

Coral Catfish (Plotosus lineatus)
• Description of danger: Spines preceding pectoral and dorsal fins are poisonous. Like members of the Scorpaenidae family, their fins are covered with an integumentary sheath of similar composition to the fin. This increases the risk of infection. There is additional toxicity, in that their skin is coated with crinotoxins (possible evolutionary precursors to the toxins in their sting). Contact can occur during aquarium maintenance or any time the animal is handled.
• Effects: Instant pain, redness and swelling around the wound. The actual wound will be pale and then turn blue. Severe reactions include swelling of the entire limb, swelling of lymph nodes and numbness. Possible gangrene if not treated. Potentially fatal.
• Treatment: Immerse the wound in hot water (43 to 45 degrees Celsius/110 to 114 degrees Fahrenheit) for 30 to 40 minutes. Be careful not to burn or scald yourself. Recommendation is to go to Emergency Room upon being stung.

Lionfish (Pterois volitans, P. sphex), dwarf lionfish (Dendochirus zebra), Fu manchu lionfish (D. biocellatus)
• Description of danger: Venom is in sack at base of dorsal, pelvic and anal spines. Spines are hollow like a hypodermic needle and sheathed in integumentary tissue. As the spine enters the victim, the sheath is compressed like a plunger into the venom sac, causing it to expel venom up the spine into the victim. The spine may break off in victim's skin and pose a greater danger than the venom in terms of infection.
• Effects: Commonly, severe pain and swelling (edema) around the wound. Less commonly, nausea, dizziness, muscle weakness, shortness of breath and hypotension. Rarely, blistering or tissue necrosis will occur. No known deaths. Possible bacterial sepsis if part of the spine remains in the flesh. Rare cases of Vibrio or Aeromonas sepsis may occur. (Smith, personal communication)
• Treatment: Lionfish venom is thermolabile and breaks down under heat (or perhaps heat eases vasoconstriction). Immerse the wound in hot water (43 to 45 degrees Celsius/110 to 114 degrees Fahrenheit) for 30 to 40 minutes. Be careful not to burn or scald yourself. Recommendation is to go to Emergency Room upon being stung.

Scorpionfish (Scorpaena)
• Description of danger: As with lionfish, venom is in sack at base of dorsal, pelvic and anal spines. Spines are hollow like a hypodermic needle and sheathed in integumentary tissue. As the spine enters the victim, the sheath is compressed like a plunger into the venom sac, causing it to expel venom up the spine into the victim. The spine may break off in victim's skin and pose a greater danger than the venom in terms of infection. Animal usually stays on ocean floor and is well-camouflaged. Envenomation occurs most frequently by people stepping on the animal.
• Effects: Same as lionfish, though the pain may be much more severe, plus shock.
• Treatment: Same as lionfish

Rabbitfish (Family Siganidae)
• Description of danger: Spines on dorsal and anal fins are poisonous.
• Effects: See scorpionfish (and lionfish).
• Treatment: Literature shows that in some rare cases, people react and may need hospitalization.

*This table is not meant to be a substitute for medical care. Aquarists should seek professional help if envenomed by a poisonous animal.

Nonenvenomating Saltwater Vertebrates

Although these animals do not carry the risk of possibly envenomating aquarists, it is still necessary to proceed with caution when around them.

Porcupinefish (family Diodontidae) and pufferfish (family Tetraontidae). These fish have beaklike teeth and will bite if cornered — and they can remove fingers. While these fish are poisonous because of an algae they eat, humans are really only at risk if they eat the fish. The poison is a tetrodotoxin. This is one of the most toxic poisons found in nature.

Triggerfish (family Balistidae). These fish have beaklike teeth and will bite if cornered. They also can remove fingers.

Moray eels (family Muraenidae). These animals may bite. The bite is often dangerous because of the possibility of secondary infection.

Boxfish (family Ostraciontidae). Boxfish have beaklike teeth and will bite if cornered. They can remove chunks of flesh. While these fish are poisonous, humans are really only at risk if they eat the fish. The poison is an ostracitoxin.

Angelfish (family Pomacanthidae). Have long, sharp spines on their gill covers, which are usually difficult to see.

Want to read the full story? Pick up the July 2008issue of Aquarium Fish International today.

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